To provide plasticity to a conventional curing agent composition of an epoxy paint and stimulate curing, alkyl phenol, particularly, nonyl phenol or a styrenated phenol compound has been used.
The alkyl phenol has an anionic molecular structure by dehydrogenating a hydroxyl hydrogen atom of phenol due to basicity of a mixed curing agent, and the generated anions have a quinone-type structure due to resonance in a molecule, resulting in changing a color to yellow or red.
According to a basicity level of the used curing agent, a degree of the discoloration is determined by a rate of being transformed into the quinone-type. When a tertiary amine curing agent having a strong basicity is used, discoloration is rapidly performed, and when a primary amine curing agent is used, discoloration may be a bit delayed, but may not be prevented.
Since the discoloration may deteriorate an exterior quality and storage stability of a product, necessity for a colorless curing agent composition may be increased, and particularly, demands for a product that can be applied to a transparent flooring material are greatly increased. However, a conventional alkyl phenol-type compound is limited to use due to chemical toxicity, and the styrenated phenol compound may also be discolored when being mixed with a curing agent.